3.1.3

• dicotyledonous


  a plant that sprouts with 2 identifiable leaves
• why do multicellular plants need a transport system?

  metabolic rate - need oxygen and glucose and removal of waste products

  small surface are to volume ratio - cannot rely on diffusion as the distance is too far

  size - contains many cells
• vascular tissue contains


  xylem and phloem
• xylem function


  transport water and ions upwards
• xylem structure

  made of lignified dead cells. This makes them waterproof and keeps them open. Lignin can be in different patterns or incomplete. Parenchyma pack around the xylem vessels

  A) one way

  B) end walls

  
• parenchyma


  cells that pack around the xylem containing food and tannin
• tannin: a chemical that protects plant tissue from herbivore
• types of lignification in the xylem vessel

  A) annular

  B) spiral

  C) reticulated

  D) pitted

  
• incomplete lignification causes


  bordered pits, that allow water to move sideways between vessels
• phloem function

  moves sap upwards and downwards
• sap


  a liquid containing sugar and amino acids
• structure of phloem

  sieve tube elements are elongated cells with perforated ends call sieve plates. They keep the phloem open and block if the sieve tube elements become damaged. Companion cells are linked to the sieve tube elements by cytoplasmic strands. They contain a nucleus and lots of mitochondria

  A) nucleus

  B) element

  C) companion

  D) plate

  
• sieve tube elements are not true cells as

  they have no nucleus and little cytoplasm
• xylem and phloem arrangement

  A) xylem

  B) phloem

  C) root

  D) shoot

  E) xylem

  F) phloem

  G) vascular bundle

  
• a plants vascular system consists of


  roots, shoots and stem
• distribution of xylem and phloem

  A) phloem

  B) xylem

  C) vascular bundle

  D) vascular bundle

  E) stele

  F) cortex

  G) pith

  
• Water transport in plants

  1. Water moves from a high potential to a low potential

  2. Plasmolysis - shrinking of cell membrane away from cell wall due to low external water potential, Allows plant cells to survive short periods of drought

  3. Turgid - Cell membrane pushing against cell wall due to high external water potential
• Root hair cells


  • Specialised exchange surface, absorb water and mineral ions
  • Large cells, many on each root
  • Maximise surface area contact with soil
• Water and mineral ion absorption by roots

  1. Water and mineral ions contained within small air spaces in soil

  2. Move into roots via osmosis as water potential of root hair cell is lower than water in soil
• Movement of water from root cells to xylem

  1. Symplast pathway (through cytoplasm, plasma membranes and plasmodesmata) the further from the roots the lower the water potential causing water to be drawn inwards and upwards

  2. Apoplast pathway (through cell walls and intercellular spaces) cohesion and tension act on cell walls pulling the water , Fastest movement is via apoplast pathway
• Casparian strip


  • Barrier stopping the apoplastic pathway
  • Made of suberin, impermeable layer
  • Forces water into symplast pathway
  • Maintains water potential gradient
• Upward movement of water in plant stem

  1. Root pressure - active transport of mineral ions into xylem, drawing water up via osmosis

  2. Cohesion-tension theory - transpiration occurs in leaves, water creates cohesion and tension, pulling water up xylem in a continuous column
• Cohesion


  Attraction of same molecules
• Adhesion


  Attraction of unlike molecules
• Water can move up the plant due to a water potential gradient, with water moving from high to low potential
• transpiration stream

  the movement of water from the roots, up the stem and to the leaves